The orbitalis muscle is a vestigial or rudimentary nonstriated muscle ( smooth muscle) that crosses from the

infraorbital groove The infraorbital groove (or sulcus) is located in the middle of the posterior part of the orbital surface of the maxilla. Its function is to act as the passage of the infraorbital artery, the infraorbital vein, and the infraorbital nerve. St ...

and sphenomaxillary fissure and is intimately united with the

periosteum The periosteum is a membrane that covers the outer surface of all bones, except at the articular surfaces (i.e. the parts within a joint space) of long bones. Endosteum lines the inner surface of the medullary cavity of all long bones. Structu ...

of the orbit. It was described by

Heinrich Müller Heinrich Müller may refer to: * Heinrich Müller (cyclist) (born 1926), Swiss cyclist * Heinrich Müller (footballer, born 1888) (1888–1957), Swiss football player and manager * Heinrich Müller (footballer, born 1909) (1909–2000), Austrian ...

and is often called Müller's muscle. It lies at the back of the orbit and spans the infraorbital fissure.Gray's Anatomy - 40th Ed/MINOR MUSCLES OF THE EYELIDS It is a thin layer of smooth muscle that bridges the inferior orbital fissure. It is supplied by sympathetic nerves, and its function is unknown.

Function

The muscle forms an important part of the lateral orbital wall in some animals and can act to change the wall's volume in lower mammals, while in humans it is not known to have any significant function, but its contraction may possibly produce a slight forward protrusion of the eyeball. Several sources have suggested a role in the autonomic regulation of the vascular system due to the pattern of innervation of the orbitalis.

Pathology

Horner's syndrome Horner's syndrome, also known as oculosympathetic paresis, is a combination of symptoms that arises when a group of nerves known as the sympathetic trunk is damaged. The signs and symptoms occur on the same side (ipsilateral) as it is a lesion ...

causes paralysis of the structures of the eye and orbit that receive sympathetic innervation. The signs of Horner's syndrome are ptosis, miosis, anhydrosis, and (apparent) enophthalmos. While some attribute the

enophthalmos Enophthalmos is a posterior displacement of the eyeball within the orbit. It is due to either enlargement of the bony orbit and/or reduction of the orbital content, this in relation to each other. It should not be confused with its opposite, ex ...

Horner's Syndrome Horner's syndrome, also known as oculosympathetic paresis, is a combination of symptoms that arises when a group of nerves known as the sympathetic trunk is damaged. The signs and symptoms occur on the same side (ipsilateral) as it is a lesion ...

to paralysis of the orbitalis muscle, this is inaccurate. Enophthalmos in Horner's syndrome is an illusion created by the subtle ptosis of the upper eyelid caused by paralysis of the

superior tarsal muscle The superior tarsal muscle is a smooth muscle adjoining the levator palpebrae superioris muscle that helps to raise the upper eyelid. Structure The superior tarsal muscle originates on the underside of levator palpebrae superioris and inser ...

. Sinking in of the eye (true ''enophthalmos'') is possibly caused by paralysis of the smooth (orbitalis) muscle in the floor of the orbit.Moore-Clinically Oriented Anatomy - Moore - 5th Ed - 2006/ part 8 : neck

Eponym

While the orbitalis muscle is also known as ''Müller's muscle'', the use of this term should be discouraged to avoid confusion with the

and the circular fibres of the

ciliary muscle The ciliary muscle is an intrinsic muscle of the eye formed as a ring of smooth muscleSchachar, Ronald A. (2012). "Anatomy and Physiology." (Chapter 4) . in the eye's middle layer, uvea (vascular layer). It controls accommodation for viewing ...

References

{{Authority control Muscles of the head and neck